Formation of isomers in the reaction 238U(p,3n)236Np.

Abstract

The energy dependence of the production cross sections in long-lived (l) and short-lived (s) isomeric states in $^{236}\mathrm{Np}$ together with the isomeric ratio of the reaction $^{238}\mathrm{U}$(p,3n${)}^{236}$Np near the reaction threshold was measured. The yield of $^{236}\mathrm{Np}^{\mathrm{s}}$ was determined from the alpha activity of $^{236}\mathrm{Pu}$ and the yield of $^{236}\mathrm{Np}^{\mathrm{l}}$ from analysis by thermal neutron fission. From the energy dependence of the isomeric ratio it follows that the long-lived state is the ground state in $^{236}\mathrm{Np}$. Theoretical calculations of the yields support these results.